Audio device, audio system, and synchronous reproduction method

ABSTRACT

An audio device includes a signal input interface, a first output interface, a second output interface, at least one processing circuit configured as a buffer control portion, at least one memory configured to store an audio signal. The buffer control portion sets a second reading position at a position that precedes a first reading position of the first output interface by delay time, and, when starting output of the audio signal, writes silent data for the delay time in the memory and sets the first reading position at the head of the silent data.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalPatent Application No. PCT/JP2016/067608, filed on Jun. 14, 2016, whichclaims priority to Japanese Patent Application No. 2015-121467, filed onJun. 16, 2015. The contents of these applications are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

Some preferred embodiments of the present invention relate to an audiodevice, an audio system, and a synchronous reproduction method thatenable a plurality of devices to synchronously reproduce an audiosignal.

2. Description of the Related Art

Conventionally, a system in which an audio signal that has beenreproduced by a master audio device is reproduced by other audio deviceshas been proposed (see Japanese Unexamined Patent ApplicationPublication No. 2006-074374, for example). In such a case, audio signalsmay be transmitted from the master audio device to other audio devicesby respective different transmission ways.

For example, a master audio device and other audio devices may be unableto reproduce an audio signal synchronously due to a difference inperformance of each of the transmission ways (for example, a differencebetween wireless transmission and wired transmission).

SUMMARY OF THE INVENTION

In view of the foregoing, some preferred embodiments of the presentinvention are directed to make it possible to reproduce an audio signalsynchronously by a plurality of audio devices.

An audio device according to some preferred embodiments of the presentinvention includes: a signal input interface configured to input anaudio signal; a first output interface; a second output interface; atleast one processing circuit configured as a buffer control portion; andat least one memory configured to store the audio signal andinstructions that, when executed by the at least one processing circuit.The buffer control portion sets a first reading position being a readingposition of the audio signal stored in the memory with respect to thefirst output interface, and a second reading position being a readingposition of the audio signal stored in the memory with respect to thesecond output interface and being a position that precedes the firstreading position by delay time. And the buffer control portion, whenstarting output of the audio signal, writes silent data for the delaytime in the memory with respect to the first output interface and setsthe first reading position at a head of the silent data.

Alternatively, an audio device according to some preferred embodimentsof the present invention includes: a signal input interface configuredto input an audio signal; a first output interface; a second outputinterface; at least one processing circuit configured as a buffercontrol portion; and at least one memory configured to store the audiosignal and instructions that, when executed by the at least oneprocessing circuit. The buffer control portion sets a first readingposition being a reading position of the audio signal stored in thememory with respect to the first output interface, a second readingposition being a reading position of the audio signal stored in thememory with respect to the second output interface, and a minimum bufferposition being a most preceding position of the audio signal in thememory; and, in a case in which, in a middle of reading the audio signalfrom the memory to the first output interface, the audio signal is newlyread from the memory to the second output interface, when a bufferamount of the memory is equal to or more than delay time, the buffercontrol portion sets the second reading position at a position thatprecedes the first reading position by the delay time, and, when thebuffer amount of the memory is less than the delay time, the buffercontrol portion sets the second reading position at the minimum bufferposition, moves the first reading position to a position that goes backfrom the minimum buffer position by the delay time, and writes silentdata for time of movement from the first reading position before themovement to the first reading position after the movement.

An audio device according to some preferred embodiments of the presentinvention is capable of reproducing an audio signal synchronously by aplurality of audio devices.

The above and other elements, features, characteristics, and advantagesof the present invention will become more apparent from the followingdetailed description of the preferred embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an audio system according to apreferred embodiment of the present invention.

FIG. 2 is a block diagram of a master device of the audio system.

FIG. 3A is a configuration diagram of a buffer of the master device, andFIG. 3B is a configuration diagram of a buffer different from the bufferof FIG. 3A.

FIG. 4A is a diagram illustrating a basic form of a buffer readingmethod, FIG. 4B is a diagram illustrating a buffer reading methoddifferent from the buffer reading method of FIG. 4A, FIG. 4C is adiagram illustrating a buffer reading method different from the bufferreading methods of both FIG. 4A and FIG. 4B, and FIG. 4D is a diagramillustrating a buffer reading method different from the buffer readingmethods of all of FIG. 4A, FIG. 4B, and FIG. 4C.

FIG. 5 is a flow chart showing an operation of an audio device.

FIG. 6 is a flow chart showing an operation of an audio device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a configuration diagram of an audio system 1 according to apreferred embodiment of the present invention. FIG. 2 is a block diagramof a master device 10.

An audio system 1 has a master device 10, a powered speaker 11 (a firstreproducing device), and one or more slave devices 12 (a secondreproducing device). The master device 10 and the slave devices 12 arecontrolled by a controller 4 through a network 3. The master device 10and the slave devices 12 are grouped. An audio signal that has beenreproduced by the master device 10 is synchronized and emitted also bythe slave devices 12.

An audio source 2 is supplied to the master device 10. The master device10 is a receiver, for example, and amplifies an input audio source 2 andoutputs the input audio source 2 to the powered speaker 11. The masterdevice 10 and the powered speaker 11 are connected to each other by adigital cable or the like and are able to transmit a high qualitydigital signal. The powered speaker 11 inputs a high quality audiosignal, and decodes and analog converts the audio signal to amplify andemit the audio signal. The slave devices 12 are each a wireless speaker,for example. The slave devices 12 are connected to the master device 10through the network 3. The network 3 includes wireless LAN such asWi-Fi. A medium quality audio signal is transmitted from the masterdevice 10 to the slave devices 12. The master device 10 transmits theaudio signal in a unicast method (TCP, for example) that performsretransmission control to the slave devices 12 in order to ensure themedium sound quality. While two slave devices 12 are illustrated in FIG.1, one master device 10 is able to be connected to nine slave devices12. In the preferred embodiment, a high quality audio signal may be a192 kbps/24 bit signal, for example, and a medium quality audio signalmay be a 48 kbps/16 bit signal, for example.

The audio source 2 is supplied from, for example, a DLNA (registeredtrademark) server or USB connected storage media (such as a hard disk orsemiconductor memory). The file format of a supplied audio source 2 maybe a FLAC (Free Lossless Audio Codec) file, for example, and satisfiesthe conditions of a high quality audio signal (192 kbps/24 bit).

FIG. 2 is a block diagram of a receiver being the master device 10. Themaster device 10 is provided with a control portion 20, a decoder 21, asampling rate converter (SRC) 22, buffers 23 and 24, a signal outputinterface 25 (first output interface), and a wireless LAN communicationinterface 26 (second output interface). The control portion 20 controlsthe whole device according to a command of the controller 4. The controlportion 20 is implemented by a CPU. The control portion 20 controls eachportion of the master device 10 by reading a program stored in a storagemedium such as a flash memory, to a work memory (RAM), and executing theprogram. The decoder 21 inputs an audio source 2 (such as a FLAC file)and decodes the audio source 2 to a streaming audio signal. The decoder21 corresponds to a signal input interface that inputs an audio signal.

The streaming audio signal is a high quality signal (192 kbps/24 bit).The audio signal that has been decoded is input to the buffer 23, and isalso input to the sampling rate converter 22. The sampling rateconverter 22 converts an input high quality audio signal (192 kbps/24bit) into a medium quality audio signal (48 kbps/16 bit). The audiosignal that has been converted is input to the buffer 24. It is to benoted that the sampling rate converter 22 is not an essentialconfiguration.

FIG. 3A is a block diagram illustrating a configuration of the buffer23. FIG. 3B is a block diagram illustrating a configuration of thebuffer 24. The buffer 23 has a memory (a first memory) 230, a writecontrol portion 231, and a read control portion 232. The buffer 24 has amemory (a second memory) 240, a write control portion 241, and a readcontrol portion 242. The memory 230 and the memory 240 may be dual portSRAM.

The write control portion 231 and the read control portion 232correspond to a first buffer control portion. The write control portion241 and the read control portion 242 correspond to a second buffercontrol portion. It is to be noted that, in the present preferredembodiment, the buffer 23 is provided with the write control portion 231and the read control portion 232 while the buffer 24 is provided withthe write control portion 241 and the read control portion 242. However,the control portion 20 to be mainly implemented by a CPU may implementthe functions of the write control portion 231, the read control portion232, the write control portion 241, and the read control portion 242. Insuch a case, the flash memory stores a program that causes the controlportion 20 to implement the functions of the write control portion 231,the read control portion 232, the write control portion 241, and theread control portion 242.

The first buffer control portion, and the second buffer control portionare executed by a processing circuit, such as a CPU (Central ProcessingUnit) or a DSP (Digital Signal Processing).

The write control portion 231 writes an audio signal from the first portof the memory 230 in the memory 230. The read control portion 232 readsthe audio signal that has been written in the memory 230 from the secondport of the memory 230. The write control portion 241 writes an audiosignal from the first port of the memory 240 to the memory 240. The readcontrol portion 242 reads the audio signal that has been written in thememory 240 from the second port of the memory 240. The details ofwriting and reading procedures will be described below with reference toFIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D.

The signal output interface 25 outputs the high quality audio signalthat has been read from the buffer 23, toward the powered speaker 11.The signal output interface 25 and the powered speaker 11 are connectedto each other by a digital cable and are able to perform high speed andhigh quality signal transmission without delay.

The wireless LAN communication interface 26 sends the medium qualityaudio signal that has been read from the buffer 24, to the slave devices12 through the network 3 (wireless LAN). Since communication with theslave devices 12 is performed by unicast as described above, thewireless LAN communication interface 26 sends the audio signal to eachof the slave devices 12, to the network 3. Therefore, a time lag occursbetween the transmission of an audio signal to the slave devices 12through the network 3 (input timing of an audio signal to the slavedevices 12) and the transmission of an audio signal to the poweredspeaker 11 through the digital cable (input timing of an audio signal tothe powered speaker 11). The input timing of an audio signal to thepowered speaker 11 is delayed behind the input timing of an audio signalto the slave devices 12 (a delay occurs). The buffer 23 and the buffer24 absorb the delay, and enable synchronous reproduction by the poweredspeaker 11 and the slave devices 12.

In order that the buffer 23 buffers a high quality audio signal, thememory 230 has a large capacity. The memory 240 of the buffer 24 is setto a capacity suited for sound quality. An audio signal to be input fromthe decoder 21 to the buffer 23 and an audio signal to be input from thesampling rate converter 22 to the buffer 24 are input in parallel at thesame time. Since the processing speed of the decoder 21 and the samplingrate converter 22 is faster than the reproduction speed of an audiosignal, the decoder 21 and the sampling rate converter 22 operateproperly according to the buffer amount of the buffer 23 and the buffer24. For example, when the buffer amount is decreased, the write controlportion 231 and the write control portion 241 respectively output abuffer underrun warning to the decoder 21 and the sampling rateconverter 22. The decoder 21 and the sampling rate converter 22, whenreceiving the buffer underrun warning, repeat processing. The readcontrol portion 232 and the read control portion 242 read an audiosignal from the memory 230 and the memory 240 at the reproduction speedof the audio signal, and then respectively output the audio signal tothe signal output interface 25 and the wireless LAN communicationinterface 26 in the following stage. It is to be noted that the amountof data read per unit time from each of the buffer 23 and the buffer 24and the amount of data required for reproduction per unit time aredifferent depending on the bit rate of an audio signal, a quantizationbit rate, and the like. Therefore, the write control portion 231, thewrite control portion 241, the read control portion 232, and the readcontrol portion 242 each require different write/read pointer control inconsideration of the difference of the bit rate of an audio signal, aquantization bit rate, and the like.

FIG. 4A, FIG. 4B, FIG. 4C, and FIG. 4D are diagrams each illustrating areading method of an audio signal that is buffered by the buffer 23 andthe buffer 24. FIG. 4A illustrates a basic form of the reading method.In the upper diagram of FIG. 4A, the read control portion 232 of thebuffer 23 reads the audio signal of time T1 (a first reading positionT1). The signal transmission system (channel A) from the signal outputinterface 25 to the powered speaker 11 has nearly no delay. Accordingly,time T1 corresponds to nearly a reproduction position of a current audiosignal. In other words, at time T1, the audio signal positioned in thefirst reading position T1 is emitted and reproduced.

On the other hand, in the lower diagram of FIG. 4A, the read controlportion 242 of the buffer 24 reads an audio signal of time T2 (a secondreading position T2) that precedes (is reproduced later) time T1 bydelay time Td. The signal transmission system (channel B) from thewireless LAN communication interface 26 to the slave devices 12 isdelayed behind the channel A. Therefore, the read control portion 242reads an audio signal that has preceded time T1 by the delay time Td,from the buffer 24, and sends the audio signal to the slave devices 12.Accordingly, the audio signal that has been synchronized by the poweredspeaker 11 and the slave devices 12 is able to be reproduced. In such acase, after time T2, audio signals after a position of the secondreading position (time) T2 of the buffer 23 are thus reproduced togetherin the channel A and the channel B. Delay occurs mainly due tocongestion of wireless LAN, retransmission control, and the throughputof inexpensive slave devices 12. During synchronous reproduction, eachdata buffer amount of the buffer 23 and the buffer 24 varies by theintermittent operation of the decoder 21 and the sampling rate converter22. However, during such synchronous reproduction, a state in which atime lag between the first reading position T1 and the second readingposition T2 is the delay time Td is maintained, and reading iscontinued.

FIG. 4B is a diagram illustrating processing at a start time ofsynchronous reproduction. FIG. 5 is a flow chart showing a flow of theprocessing illustrated in FIG. 4B. The processing of FIG. 4B isperformed when the powered speaker 11 and the slave devices 12 performsynchronous reproduction from the start time (beginning of music, forexample) of the reproduction of the audio source 2. In other words, theprocessing of FIG. 4B is performed when the output of an audio signal isstarted.

To begin with, the decoder 21 inputs an audio signal (S11). The writecontrol portion 231 and the write control portion 241 write the audiosignal in the memory 230 and the memory 240, respectively, and cause thebuffer 23 and the buffer 24 to temporarily store the audio signal (S12).

The write control portion 231 writes silent data (zero data) for delaytime Td (zero data) in the buffer 23 of the channel A in advance ofreproduction start (S13). This is because, at the beginning of music, inother words, at a time of no previous audio signal, the first readingposition T1 of the channel A is caused to synchronize with a positionthat goes back from the second reading position T2 of the channel B bythe delay time Td.

The read control portion 232 sets the first reading position T1 to thehead of the silent data (S14). Then, the read control portion 242 setsthe second reading position T2 at a position that precedes the firstreading position T1 by the delay time Td (S15).

The read control portion 232 and the read control portion 242 determinewhether or not the minimum audio signal required for reproduction startthereafter is buffered (S16). The read control portion 232, whendetermining that the minimum audio signal has been buffered, readssilent data from the first reading position T1. In the buffer 24 of thechannel B, the read control portion 242 starts reading from the head ofan audio signal. Accordingly, an audio signal is output both from thesignal output interface 25 being the first output interface and thewireless LAN communication interface 26 being the second outputinterface (S17). In the buffer 23 of the channel A, the read controlportion 232 starts reading from the head of the silent data that goesback therefrom by the delay time Td. The powered speaker 11 of thechannel A reproduces the head of an actual audio signal afterreproducing the silent data for the delay time Td. In addition, theslave devices 12 start reproducing with delay by the delay time Td dueto the difference in transmission rate from the channel A and thedifference in reproduction ability from the powered speaker 11.Accordingly, the powered speaker 11 and the slave devices 12 performsynchronous reproduction thereafter.

FIG. 4C and FIG. 4D illustrate processing in a case in which synchronousreproduction of the slave devices 12 (channel B) is caused to start inthe middle while the powered speaker 11 (channel A) reproduces an audiosignal. FIG. 6 is a flow chart showing the flow of processing of FIG. 4Cand FIG. 4D. In the processing of FIG. 4C and FIG. 4D, while the readcontrol portion 232 causes the signal output interface 25 to read anaudio signal from the buffer 23, the read control portion 242 causes thewireless LAN communication interface 26 to newly read an audio signalfrom the buffer 24. FIG. 4C illustrates a reading form in a case inwhich the buffer amount of the buffer 23 and the buffer 24 is equal toor more than the delay time and synchronous reproduction by the slavedevices 12 is able to be started while the reproduction by the poweredspeaker 11 continues. FIG. 4D illustrates a reading form in a case inwhich the buffer amount of the buffer 23 and the buffer 24 is less thanthe delay time and the powered speaker 11 temporarily stops reproductionto start reproducing in synchronization with the slave devices 12.

The decoder 21 inputs an audio signal (S21). The write control portion231 and the write control portion 241 write the audio signal in thememory 230 and the memory 240, respectively, and cause the buffer 23 andthe buffer 24 to temporarily store the audio signal (S22). Even whenreproduction by the slave devices 12 is not performed, the audio signalis continuously written in the buffer 24 from the sampling rateconverter 22. Further, a buffered audio signal is not read and is thrownaway (overwritten) in order from the oldest audio signal.

The read control portion 232 sets the first reading position T1 (S23),and outputs an audio signal from the signal output interface 25 beingthe first output interface (S24). The first reading position T1 here isset at the head of the buffered audio signal. However, the audio signalis output when data for the minimum buffer required for at leastreproduction start is buffered in the memory 230.

If an instruction of reproduction by the slave devices 12 is input fromthe controller 4 while the signal output interface 25 outputs an audiosignal toward the powered speaker 11 (S25), the control portion 20refers to the buffer amount of the buffer 23 and the buffer 24 (S26).Then, the control portion 20 determines whether or not the buffer amountof the buffer 23 and the buffer 24 is equal to or more than the delaytime (S27). If the buffer amount of the buffer 23 and the buffer 24 isequal to or more than the delay time, the read control portion 242performs processing from step S28 to step S30. If the buffer amount ofthe buffer 23 and the buffer 24 is less than the delay time, the writecontrol portion 231, the read control portion 232, and the read controlportion 242 perform processing from step S41 to step S45.

To begin with, in the processing of step S28, the read control portion242, as illustrated in FIG. 4C, refers to the first reading position T1of the buffer 23 at that time and sets the second reading position T2 ata position that precedes from the first reading position T1 by the delaytime Td. In addition, the read control portion 242 discards the bufferdata of the buffer 24 before the second reading position T2 (S29). Theaudio signal that has been read from the buffer 24 is sent to the slavedevices 12 through the network 3 (S30). Accordingly, the reproductionsound of the powered speaker 11 is not interrupted and synchronousreproduction is started in the middle (after time T2) in the slavedevices 12.

On the other hand, the read control portion 242, in the case of beingunable to ensure the minimum buffer if causing a reading position T3 ofthe buffer 23 at that time to precede in the buffer 24 by the delay timeTd, sets the second reading position T2 of the buffer 24 at the minimumbuffer position being the most preceding position of the audio signal inthe buffer 24 (S41). In addition, the read control portion 242 discardsthe buffer data of the buffer 24 before the second reading position T2(S42).

Then, the first reading position T1 of the buffer 23 is set at aposition that goes back from the second reading position T2 by the delaytime Td (S43). However, the first reading position T1 is a past positionprior to a current reading position T3, and the audio signal of the pastposition has been already read. Accordingly, the write control portion231 adds silent data from the first reading position before movement(the current reading position T3) to the first reading position T1 thathas been moved this time (S44).

Then, the read control portion 232 and the read control portion 242simultaneously start reading an audio signal each from the first readingposition T1 and the second reading position T2 of the buffer 23 and thebuffer 24 (S45). Thus, the silent data is read first for a short time inthe buffer 23, and sound is interrupted for a short time in the poweredspeaker 11. Subsequently, the audio signal that corresponds to time ofthe reading position T3 to the second reading position T2 by the poweredspeaker 11 is reproduced independently, and, after the time of thesecond reading position T2, is started reproducing synchronously by thepowered speaker 11 and the slave devices 12.

The delay time Td may be previously set in the master device 10 at thetime of shipment from a factory. Alternatively, the delay time Td may beset with a controller 4 by a user estimating a synchronous lag whilelistening to reproduction sound. In addition, in a case in which themaster device 10 and the slave devices 12 are synchronized with eachother with respect to internal time, the delay time Td may not be setwith high precision as long as the reproduction time (absolute time) ofan audio signal is added with a time stamp.

In the above preferred embodiment of the present invention, as long asthe bit rate of the channel A and the channel B and a quantization bitrate are the same, the number of buffers may be one. In such a case, thebuffer control portion (read control portion) may cause the channel Aand the channel B to read buffer data from a separate address.

While, in the above preferred embodiment of the present invention, thepowered speaker 11 is connected to the master device 10 by the digitalcable, the powered speaker 11 as well as the slave devices 12 (as one ofthe slave apparatus 12) may be connected to the master device 10 throughthe network 3.

While, in FIG. 4D, when the buffer amount of the buffer 23 and thebuffer 24 is insufficient, silent data is written in the buffer 23,synchronous reproduction may be started after the decoder 21 and thesampling rate converter 22 are started to make the buffer amount of anaudio signal necessary and sufficient (after being a state in FIG. 4C).

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An audio device comprising: a signal inputinterface configured to input an audio signal; a first output interface;a second output interface; at least one processing circuit configured asa buffer control portion; and at least one memory configured to storethe audio signal and instructions that, when executed by the at leastone processing circuit, wherein: the buffer control portion sets a firstreading position being a reading position of the audio signal stored inthe memory with respect to the first output interface, and a secondreading position being a reading position of the audio signal stored inthe memory with respect to the second output interface and being aposition that precedes the first reading position by delay time; and thebuffer control portion, when starting output of the audio signal, writessilent data for the delay time in the memory with respect to the firstoutput interface and sets the first reading position at a head of thesilent data.
 2. An audio device comprising: a signal input interfaceconfigured to input an audio signal; a first output interface; a secondoutput interface; at least one processing circuit configured as a buffercontrol portion; and at least one memory configured to store the audiosignal and instruction that, when executed by the at least oneprocessing circuit, wherein: the buffer control portion sets a firstreading position being a reading position of the audio signal stored inthe memory with respect to the first output interface, a second readingposition being a reading position of the audio signal stored in thememory with respect to the second output interface, and a minimum bufferposition being a most preceding position of the audio signal in thememory; and in a case in which, in a middle of reading the audio signalfrom the memory to the first output interface, the audio signal is newlyread from the memory to the second output interface, when a bufferamount of the memory is equal to or more than delay time, the buffercontrol portion sets the second reading position at a position thatprecedes the first reading position by the delay time, and, when thebuffer amount of the memory is less than the delay time, the buffercontrol portion sets the second reading position at the minimum bufferposition, moves the first reading position to a position that goes backfrom the minimum buffer position by the delay time, and writes silentdata for time of movement from the first reading position before themovement to the first reading position after the movement.
 3. The audiodevice according to claim 1, wherein the memory includes: a firstmemory; and a second memory; the at least one processing circuit isfurther configured to: write the audio signal in the first memory andthe second memory; and read the audio signal from the memory; the firstreading position is set in the first memory; and the second readingposition is set in the second memory.
 4. The audio device according toclaim 2, wherein the memory includes: a first memory; and a secondmemory; the at least one processing circuit is further configured to:write the audio signal in the first memory and the second memory; andread the audio signal from the memory; the first reading position is setin the first memory; and the second reading position is set in thesecond memory.
 5. The audio device according to claim 3, wherein the atleast one processing circuit is further configured to discard the audiosignal before the second reading position in the second memory.
 6. Theaudio device according to claim 4, wherein the at least one processingcircuit is further configured to discard the audio signal before thesecond reading position in the second memory.
 7. An audio systemcomprising: the audio device according to claim 1; a first reproducingdevice configured to reproduce the audio signal that is output from thefirst output interface; and a second reproducing device configured toreproduce the audio signal that is output from the second outputinterface, wherein the delay time corresponds to a time lag betweeninput of the audio signal to the first reproducing device and input ofthe audio signal to the second reproducing device.
 8. An audio systemcomprising: the audio device according to claim 2; a first reproducingdevice configured to reproduce the audio signal that is output from thefirst output interface; and a second reproducing device configured toreproduce the audio signal that is output from the second outputinterface, wherein the delay time corresponds to a time lag betweeninput of the audio signal to the first reproducing device and input ofthe audio signal to the second reproducing device.
 9. The audio systemaccording to claim 7, wherein a transmission system from the firstoutput interface to the first reproducing device and a transmissionsystem from the second output interface to the second reproducing devicehave different transmission rates.
 10. The audio system according toclaim 8, wherein a transmission system from the first output interfaceto the first reproducing device and a transmission system from thesecond output interface to the second reproducing device have differenttransmission rates.
 11. A synchronous reproduction method comprising:inputting an audio signal; storing an input audio signal; and whenstarting output by reading a temporarily stored audio signal from afirst reading position and a second reading position, writing silentdata for delay time in front of the temporarily stored audio signal,setting the first reading position at the head of the silent data, andsetting the second reading position at a position that precedes thefirst reading position by the delay time.
 12. The synchronousreproduction method according to claim 11, further comprising: readingthe audio signal from a first memory; reading the audio signal from asecond memory; writing the audio signal in the first memory; writing theaudio signal in the second memory; setting the first reading position inthe first memory; and setting the second reading position in the secondmemory.
 13. The synchronous reproduction method according to claim 12,further comprising discarding the audio signal before the second readingposition in the second memory.